1. Technical Field
The invention relates to air brake systems for motor vehicles and more particularly to an automated monitoring system for air supply systems used with truck air brakes systems.
2. Description of the Problem
Air compressors on trucks supply pressurized air to a storage system which in turn supports the operation of an air brake system for the truck and trailers pulled by the truck. Other vehicle systems such as air suspension systems may also tap the storage system for air. The periodic testing of the compressor and the air storage and distribution system promotes safe operation of vehicles using such systems. Government motor vehicle regulations set forth operating standards for air compressor systems and require periodic testing before commercial operation of these vehicles.
The air compressor on a truck is typically under the control of a governor which triggers compressor operation in response to falling system pressure. The point where compressor operation engages is called the cut-in pressure. The governor further responds to pressure in the system reaching an upper limit at which point it causes the air compressor to discontinue supplying pressurized air. This point is called the cut-out pressure.
Air compressor system performance varies by manufacturer, by age of the system and by its state of repair. Systems differ in the number of compressed air tanks and in the capacity of the tanks. Some vehicles are equipped with air suspensions which make independent demands on available compressed air. Leakage rates vary from system to system. When new or in good repair an air compressor system should operate at close to its optimal levels. With age and deterioration of the system, the system may come to fall short of these optimal operating values. Inspection regimens should detect failure of a system to operate close to original specification as an indicator of potential failure.
Inspection regimens must be established to comply with government regulations. These regimens check variables such as compressor governor cut-out, governor cut-in and monitor gauge pressure against a clock to determine charge and leak rates. A representative procedure requires a driver or operator to:
“Check Air Compressor Governor Cut-in and Cut-out Pressures. Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut-out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise.”“Test Air Leakage Rate. With a fully-charged system (typically 125 psi), turn off the engine, release the service brake, and time the air pressure drop. The loss rate should be less than two p.s.i. in one minute for single vehicles and less than three p.s.i. in one minute for combination vehicles. Then apply 90 p.s.i. or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three p.s.i. in one minute for single vehicles (more than four p.s.i. for combination vehicles), the air loss rate is too much. Check for air leaks and fix before driving vehicle. Otherwise, you could lose your brakes while driving”.“Check Rate of Air Pressure Buildup. When the engine is at operating rpm, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe. Check the manufacturer's specifications.) In single airsystems (pre-1975), typical requirements are pressure buildup from 50 to 90 psi within three minutes with the engine at an idle speed of 600-900 rpm.”Making these determinations both manually and daily is obviously time consuming. In addition, the or if insufficient date pressure gauges used in making the tests are frequently imprecise and difficult to read.